Understanding Water Flow in Natural and Artificial Channels
Understanding Water Flow in Channels
Natural vs. Artificial Channels
To calculate using equations of Saint-Venant, consider the following:
- Cauce Natural Irregularity: Track Section Slope Roughness
- To study the movement of water in natural channels, it is necessary to divide it into homogeneous sections obtained by mathematical formulation values of hydraulic variables in each section.
RIVER HYDRAULIC: Focuses on the study of flow variations due to weather and mobility of the bed.
ARTIFICIAL CAUCE Canal: The artificial channel created and controlled by man with simple design criteria allowing for more accurate estimates. The water transport channels are dimensioned in steady and uniform flow.
Types of Artificial Canals
CANAL:
- Binoculars: one whose slope and cross section are constant.
- Keystone: is used in unstable ground.
- Rectangular: for more stable ground.
- Triangular: is used in irrigation channels. Little used.
- Circular: prefabricated pipes.
- Ovoid: sewage networks.
The speed in a section is not uniform, but in the fixed contours, the velocity is zero at the free surface is equal to the air in contact, and increases as it moves away from the contours.
The velocity field depends on:
- The geometry of the section
- Roughness outlines
Isotach curves describe for us the points of the section of the same speed. At the free surface, air speed imposes velocity of water. If air movement is rapid, it can excite the formation of waves. Normally water channels move faster than air and thus hinders the contact as in Figure curved path in channels on the ground will cause an acceleration of flow in the outer side of the curve as a result of centrifugal force.
If the disturbance on a current that moves at a speed v < c, the wave propagates upstream at a speed vc. In this case Fr < 1 and the movement is called in SYSTEM SLOW.
If the disturbance on a current that moves at a speed v = c, the upstream wave will be stationary. In this case Fr = 1 and the movement is called the critical regime.
If the disturbance on a current that moves at a speed v > c will not propagate upstream. In this case F > 1 and the movement is called the rapid rate.
Relationship Between Flow and Depth
RELATIONSHIP FLOW DEPTH: Depth ratio under variable flow are not one-one as in steady and uniform. Depending on the predominant forces this matter will be higher or lower. With dominance of inertial forces (velocity change) and pressure (depth variation) the greater the difference from the steady and uniform. With dominance of the forces of weight (slope) and friction (roughness) are closer to the corners. This is the case of rivers which allows us to manage cost curves without much error.
The transport channels normally have LINER, unless resources are abundant and cheap, and geotechnical has good sealing ability, those avenues are made without lining. The lining gets: cutting costs, load losses, infiltration, prevent erosion.
- Trapezoidal vegetation: the most used
- Circular: best hydraulic conditions, execution more complicated
- Rectangular: a bit is used in the channels used for disposal of mechanical design of lined canals V < 2.5 m / s, except in special projects and other rapid loss high, where speed can be very superior.
Unlined channels, the maximum speed is limited at the start of drag.
Drainage mission is to eliminate internal uplift pressures is achieved by depressing the water table along the lining.
Concrete Coating
The coating thickness varies between 10 and 20 cm depending on the size of the channel would normally go to a thickness of 15 cm concrete-lined channels may have four types of construction joints are as shown because to stop concreting. It is best to coincide with another meeting.
Expansion joints are not normally required in a coating of concrete, except when there are fixed structures that intercept the channel.
Transverse contraction joints are placed to avoid cracking of the coating caused by shrinkage of setting.
Longitudinal contraction joints are required in sections executed in mass concrete, provided that the perimeter of the lining exceed 9 m.
Expansion joints are not normally require a concrete lining, except when there are fixed structures that intercept the channel.